The present invention relates to an improvement in the use of adsorbent particles on a support structure so as to form a flexible adsorbent filter media.
U.S. Pat. No. 5,332,426 describes a self-supporting filter formed of agglomerated adsorptive particles, which adsorbent is preferably activated carbon. The carbon or other similar adsorptive materials are preheated to a temperature generally above the softening temperature of the binder particles. The binder particles are then added under mixing conditions resulting in the formation of agglomerates of the binder and adsorbents. The binder particles are attached to the surface of the adsorptive particles which results in the formation of agglomerates. The agglomerates can then be further joined to each other under heat and optionally a certain amount of pressure to directly form an adsorbent filter. The direct mixing of binder and activated carbon and the like to form a filter is described in U.S. Pat. No. 3,538,020. In this case, the carbon and binder are directly formed into a filter without the intermediate formation of agglomerates. In this patent, the carbon or adsorbent particles are joined directly to each other. This results in a higher concentration of carbon, but the pressure drop is very high and unacceptable for many uses. In either method where adsorbants are bonded to each other to form a filter, the resulting filter is rigid so that it has to be directly formed into its final intended end use shape, which is complicated and expensive for non-flat filter structures.
Activated carbon or other adsorptive particles have also been attached to supporting structures, such as disclosed in U.S. Pat. No. 4,906,263. In this patent, a carrier framework, comprised of wires, monofilaments or stays, is coated with an adhesive or binder. After the binder is in place, activated carbon or like adsorptive particles are added and attached to the support structure. This patent describes that the distances between the structural elements of the support structure are large enough so as to allow the carbon particles to interpenetrate into the depth of the structure covering the support or structural elements. The carrier framework described in this patent is preferably from three to ten times as open as the diameter of the adsorbent particles to provide a highly air permeable filter. The filter media is described as designed to be stable in shape. The support structures are specifically described as reticulated foams with a pore size of 1.5 mm to 4 mm, a lattice of wire mesh with a mesh width of 1 mm to 5 mm, spirally wound wires with a spiral diameter of 0.3 mm to 10 mm, or fiber brushes. The wire mesh or the reticulated foams can be formed into sheets, but these sheets are not readily bendable without substantial deformation of compression of the pore structure. A similar-type support structure is disclosed in U.S. Pat. No. 6,207,255.
It is also known to physically entrap carbon particles and the like within a support structure, such as disclosed in U.S. Pat. No. 4,081,501. In this patent, carbon particles or the like are mixed with air and forced into a fibrous web, although an adhesive can be added for further binding, the adsorbent particles penetrate into the support structure under the force of the air pressure and become entrapped. In U.S. Pat. Nos. 3,971,373 and 4,433,024 binder particles are structurally entrained in a blown microfiber web by introducing particles into the fiber stream prior to collection of the fibers as a coherent web. This method allows a large quantity of adsorbent particles to be contained within a matrix where the particles can comprise up to 99% of the web structure and then can be joined to a further layer.
U.S. Pat. No. 5,486,410 describes forming a web from composite fibers consisting of a structural component and a lower-melting binding component. The web is heated to melt or soften the binding component, which acts as an adhesive, prior to applying the adsorbent particles.
These nonwoven fiber-based adsorbent filters are very dense structures and exhibit high-pressure drops similar to filters where the adsorbent particles are directly bonded each to the other. The nonwoven-based webs are generally flexible but are not shape retaining and can become easily compressed when bent or deformed about a radius of curvature.
There is a need for extremely open adsorbent filters, such as those described by U.S. Pat. No. 4,906,263, which also can be bent or deformed out of a plane without significantly affecting the pressure drop performance of these filter structures. Flexible or deformable high air flow filters would find use particularly where significant pressure drops are not acceptable such as air conditioners, automotive cabin air filters, furnace filters, and the like. In these uses there is often limited space for large flat filters, and there is a need to avoid significant pressure drops, which could result in significant health or safety concerns. However for manufacturing, transportation, packaging, and marketing reasons it is desirable that filters be flat prior to use and then assume a three-dimension form when used, by flexing, without a subsequent large increase in pressure drop due to deformation or consolidation of the filter pore structure when the filter is bent.
The invention comprises a flexible adsorbent-loaded filter formed from a flexible support web and attached adsorbent particles. The adsorbent-loaded filter has open filter cells which are defined by the support web and the attached adsorbent particles and are random in size and orientation through the length and depth of the filter. The support web is formed of substantially nonlinear filaments that randomly intersect. The adsorbent particles largest average cross sectional dimension is smaller than the average diameter of the pores of the support web. When the flexible adsorbent loaded filter is flexed about a radius of curvature 20 mm, the percent increase in pressure drop is less than 100 percent when measured at a face velocity of 0.25 m/s.